Disclosed herein is a vehicle seat, and particularly a vehicle seat including a seat back that supports a seated passenger from the rear.
One indicator of the performance required for vehicle seats is that the posture (the seating posture) of a seated passenger is stably maintained, and some techniques satisfying such a need have been already developed (see, e.g., Japanese Patent Document No. 2000-095000 A (“the '000 Document”). In the vehicle seat described in the '000 Document, each shoulder portion of a seat back includes a protective bag. This protective bag expands forward in a raised shape to cover around the shoulders of a seated passenger from the above toward the front, thereby engaging with the shoulders of the seated passenger. As a result, the posture of the seated passenger is stably maintained, and in particular, upward movements of the upper body of the seated passenger can be reduced.
In the vehicle seat described in the '000 Document, the above-described protective bags expand when an excessive load is input to the seat due to, e.g., rear-end collision, and are used as the device for protecting the seated passenger in emergency situations. It is also required for a normal vehicle running situation to hold the shoulders of the seated passenger to maintain the posture of the seated passenger as in the vehicle seat described in the '000 Document. More specifically, of the pressure applied to the seat back in a seated state, the pressure applied to the portions supporting the shoulders of the seated passenger is relatively high, and therefore, the posture of the seated passenger can be stabilized in such a manner that the shoulders of the seated passenger are held while a vehicle is running. In order to provide such an advantage, it is required to properly hold the shoulders of the seated passenger while the vehicle is running.
In the configuration in which, as described in the '000 Document, the protective bags cover around the shoulders of the seated passenger from the above toward the front to engage with the shoulders of the seated passenger, forward movement and upward movement of the body of the seated passenger can be restricted, but it is difficult to restrict movement in the right-to-left direction (i.e., in the width direction of the seat). As long as movement of the upper body of the seated passenger in the right-to-left direction cannot be properly restricted, it is difficult to stabilize the posture of the seated passenger.
Moreover, when the shoulders of the seated passenger are held only by the protective bags in order to maintain the posture of the seated passenger, sufficiently-large protective bags are required to hold the shoulders of the seated passenger. This leads to an increase in the size of the protective bag and the size of the mechanism for expanding the protective bag.